powell



W. T. POWELL.

AUTOMATIC TELEPHONE SYSTEM APPLICATION HLED APR. 14, 1917.

1,356,010. Y Patnted 00g 19,1920.

6 SHEETS-SHEET 1.

W. T. POWELL.

AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED APR. 14. 1911.

1,356,010. Patented Oct. 19,1920.

6 SHEETSSHEET 2.

W. T. POWELL.

AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED APR.14, 1917.

1,356,010,. Patented Oct. 19,1920.

6 SHEETSSHEET 3.

W. T. POWELL.

AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED APR. 14, 191i.

Patented M19, 1920.

W. T. POWELL.

AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED APR-14, 1911.

Patented 0ct.19, 1920.

6 SHEETSSHEET 6.

UNITED STATES PATENT OFFICE."

WINFRED T. POWELL, OF CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS. 7

AUTOMATIC TELEPHONE SYSTEM.

Patented Oct. 19, 1920.

Application filed A ril 14, 1917. Serial No. 161,956.

To al whom it may concern Be it known that I, l/VINFRED T. POWELL,

a citizen of the United States of America,

and resident of Chicago, Cook county, Illinois, have invented certain new and useful by toll lines, the long distance connections being established preferably through the medium of automatic switches; and the ob iect of the invention is to provide new and improved circuits for automatic private branch exchanges included in a system of the above general character, with a. view to providing talking circuits of maximum efficiency. and introducing numerous new and advantageous operating features which add appreciably to the quality of the service.

All the different phases of my invention, and the preferred method of constructing and using the same, will be fully described hereinafter, reference being had to the accompanying drawings, comprising Figures 1 to (3. inclusive, which show in diagrammatic form the essential circuits of a system embodying the principles of my invention.

For a clear understanding of the drawings they should be placed inorder with the lines at the ends thereof inalinement, and p when thus arranged there is shown a complete circuit connection extendingfrom the toll line 23 in Fig. 1 to the automatic private branch exchange substation A in Fig. -l. The connection has been established through the medium of the toll operators cord circuit 0, Fig. 1; the toll first selector V, Fig. 2; the toll second selector W; the combination toll local repeater F, Fig. 3; the two way trunk line comprising conductors 233, 234: and235, connecting the main exchange with the private branch exchange, and extending through the attendant onerators key circuit M, Fig. 4-: the

special incoming selector E. Fig. 5; and the special toll connector H, Fig. 6.

The selector and connector switches in the system are preferably of the well known Stronger vertical and rotary type, the mechanical construction of which is disclosed in the U. S. patents to Keith,.Erickson, and

Erickson Nos. 815,821, and 815,176, both granted March 13, 1906. In the selector switches, however. the side switches and private magnets have been omitted. and all circuits, including the connector circuits,

have been revised in accordance with mod-' ern two-wire practice. There are of course other modifications having to do more particularly with the various features of the invention, all of which will be described in detail hereinafter.

The apparatus shown in Figs. 1 and 2 forms no part of my invention and is shown onlyto facilitate the understanding of its operation. In Fig. 1, the reference characters 2 and 3 indicate a toll line of some kind which may extend to a distant point. It terminates at the toll switch board in a jack J, and in the usual multiple jacks (not shown). The associated equipment shown in the drawing, comprising the dropo and cut-off relay 1-, is of the simplest type, and may be replaced or supplemented byany well. known apparatus as desired.

The cord circuit 0 may likewise be of any suitable type, although the calling end must be arranged to cooperate with the toll service trunks. A single supervisory bridge comprising the lowerwinding of the ringing up and locking relay 8, the condenser 12, and the impedance coil 7 is connected across the two strands of the cord circuit and controls the supervisory lamp L The lamp L is the answering supervisory lamp and is controlled by the marginal sleeve relay 9, while the lamp Lis a special supervisory signal controlled by the same relay and whose function it is to inform the operator when a busy line has become idle, all of which will be explained fully hereinafter. Keys K and K are the regular ringing keys. The double throw key K is a combined listening and monitoring key. When thrown in one direction the operators head set is bridged across the two strands of the cord circuit in the regular manner, but when thrown in the opposite direction the relay 13 is operated. wherebythe'receiver in series with the resistance 14 is connected'across the cord circuit for .monitoring purposes. The double throwkey K is provided toen able the operator to open the cord circuit conductors on either side of her listening key. whereby she is able to cut-of! the subscriber at either end while talking to the subscriber at the other end. The function of key K is to shift the control of the relay 9 from lamp L to lamp L. The key K is a calling device key through the medium of which the operator may insert the calling device S in the sleeve conductor of the cord. The calling device S may be common to a number of cord circuits, and is of the well known two wire type, such as is disclosed in the British patent to Dicker, No. 29654 of 1910.

For the purpose of completing toll connections to local subscribers lines, each toll operator has before her multiple jacks off a group of so-called toll service trunks each of which extends to a toll first selector. A complete toll trunking system involving toll service trunks of the character shown in this application is disclosed in the prior ap plication of John lVicks, Serial Number 124,358, Patent No. 1,315,444:, September 9, 1 919, and accordingly this portion of the equipment need not be described in detail. It will suffice to say, referring to the drawing's, thatthe operator who has the cord circuit O, has in front of her a plurality of multiple jacks. one of which is the jack J,

from which trunk lines extend to toll first selectors, one of which is the selector V. The toll first selectors have access to trunk lines terminating in toll second selectors, such as the selector V; and the toll second selectors in turn have access to trunk lines which terminate in connectors having access to the local subscribers lines in the main exchange. These connector switches are not shown, but it may be mentioned are accessible also from the second selectors of the regular main exchange trunking system. It desired the toll second sclcctorsmay also be accessible to incoming toll selector repeatersof the type shown in the prcviouslv mentioned application of icks, and a multiple which may extend to the bank of one of these selector repeaters is shown at the top of Fig. 2'; but since my invention is not limited to use in connection with any particular trunking system it has been thought unnecessary to show all these details.

Having explained briefly the general layout of the main exchange, attention will now be directed to the equipment of the branch exchange. The automatic private branch exchange partially shown in Figs. 4,

5 and 6, is a three digit system, that is, local connections are established through the medium oi first selectors and conuectori-r, and ordinarily the capacity would be 1000 lines. Since the tenth level of the selectors however is reserved for calling the main exchange, the actual capacity is 900 lines. The branch exchange then may be considered as being fundamentally a standard automatic exchange provided with first selectors and connectors. As is customary, the subscribers lines are given access to the selector switches through the medium of individual line or trunk selecting switches which will be more particularly referred to later. In addition to the local trunking system briefly described abovc, the branch exchange is connected with the main exchange by trunk lines; and is also provided with an attendant operators switchboard. Each trunk line connecting the main exchange with the branch exchange goes through a key circuit at this switchboard, whereby the attendant operator is enabled to exercise a control over the connections established thercover; and it is this control, which may be only of a supervisory nature, or which may consist of actual participation in the establishment of connect-ions, which forms some of the principal subject matter of the invention. In addition to the trunk line key circuits, the attendants switchboard is provided with a few other key circuits which are for the purpose of giving special service to importhan subscribers at the branch exchange. For example, assuming that the branch exchange is installed in a large manufacturing es-' tablishment, the important officials oi the company will usually demand a special service, which on account of the expense it would be impracticable to give to the great majority of the telephone users. The lines from the telephones of these oiiicials therefore are extended through special key circuits at the attendants switchboard before they terminate in their individual line switches.

This may be more readily understood by a consideration of the line of substation A. Fig. 4, which is assumed to be a special service line. The telephone instrument itself may be of any approved common bat tery type, and as shown herein comprises the receiver 602, transmitter 603, switchhook 604:, ringer 605, and condenser 60G. Being an automatic substation there is also provided a calling device, represented. here in by the impulse springs 607 and 608 and the impulse wheel 609, which may be of the type disclosed in the British patent to icker previously referred to.

The line conductors 612 and 613 extend to the attendants switchboard, where they pass throu 11 contacts in the key circuit equipment before continuing by way of conductors 650 and 653 to the individual line switch C, Fig. 5. The key circuit N comprises a group of relays whose functions will be described later, the line and supervisory lamps L and L and three keys. (if these latter, the key K is a ringing hey; the double throw key K is a combined listeningand calling device key; while the key K is a combined release and restricted service key.

The individual line switch C and the masnectiiur trunk lines and its accessories is shown. complete, the trunk line proper be-.

ter switch D, Fig. 5, are of the type disclosed in U. S. Letters Patent No. 1,078,690,

granted J an. 17, 1912, to Frank Newtorth,

it will be understoodpserves to control the line switch C and other similar line switches inthe selection of idle selector switches.

The selector E and the connector H, as before mentioned, are of the well known Strowogcr vertical and rotary type and need no description other than that which will be given in the description oi the operation of the svstem.

Both the'main and branch exchanges havwill new contwo are intering been brietly described we sider the means by which the connected, In the description of the trunking in the main exchange it was explained that the toll second selectors such as the selector lV, Fig. 2, had access to groups of connector switches which in turn had access to subscribers lines, these connectors being also accessible to second selectors ot the regular main exchange trunking system,

Where there are private exchanges subsidiary to the main exchange, however, as in extending to the connector switches, but a certain level as "for example the teuthlevel, is set apart for the branch exchange trunks,

Of course the corresponding level in the regular second selectors will. also be reserved for the same purpose.

In 3, 4t, and 5, one of the interconinc indicated by the reference characters 233, 22 3i, and 235. At the main exchange it has two branches, one oi. which terminates in the repeater ll, and the other in the line switch C. The repeater F comprises a group oi relays whose functions willbe de scribed later; and 1S accessible to the toll second selectors SllCll flS the selector W, Fig.1

2, and also to the second selectors ot the regular main exchange trunking system,

thus torming the 1 cans by which selectors of both kinds are given access to the associated trunk line. In the case of the selecs ment ill,

tor W and similar toll second selectors, connection may be extended to the repeater F and thence to the trunk line under consldoration byway oi the trunk conductors case there are a plurality of branch ex.-

changes, however, it will be understood that third selectors may be interposed in order to handle the plurality of groups of trunk lines which would then be necessary.

The line switch C affords means whereby connections from the branch exchange may be extended to subscribers in the main exchange byway otthe regular main exchange trunking system. The line switch C is similar to the line switch C, Fig. 5, already described, and has access to selector switches over a group ottrunk lines, one of which, comprising the connectors 241, 242, and 243, is partiallv shown to the left of the line switch. 1

At the branch exchange the conductors 23 i, and of the interconnecting trunk line extend by way of contacts in the key circuit equipment M, Fig. 4:, to the conductors 380, 382,, and 389, respectively, which terminate in the incoming selector E, 5; there being also a branch comprising the conductors 750, 386, and 7 51, which extends to multiple contact sets in the tenth level of the local first selectors such as the selector E. The key circuit equipment M comprises the group of relays 300 to 304-, inclusive; tour lamp signals, comprising the nisy lamp L, the line lamp Lfl-the guard lamp L and the supervisory lamp L; and five keys, of which the key K is a combined release and calling device out key, key K is a special. key which I term a hold key, key K is a combined listening and calling device in key, key K is a special key which will be referred to hereafter as acall through key, and key it is a release in key. The explanation of the functions of these relays, lamps, and keys can best be made by cescribing the operation of the system and will theretore be deferred until l ater.

the invention, and particularly in view of the contemplated inter-dependency between the selector switch and the key circuit equipiAt this time mention should be made of the three sets of shaft controlled springs shown in the drawing ust below the relays of the switch. The springs 460, 461, and 462 may be termed tenth level off normal springs; in other words, when the shaft arrives at the tenth level spring 461 is shifted from engagement with spring 460 into engagement with spring 462. The springs 463 to 468, inclusive, are the regular of? normal springs and are closed together in pairs upon the first upward movement of the switch shaft. The springs 470 to 473, inclusive, are rotary off normal springs, and are actuated upon the eleventh rotary step of the shaft by any suitable cam arrangement.

The banks of the incoming selectors such as the selector E are not multipled with the banks of the local selectors such as the selector E, but contain terminals of separate groups of trunk lines which extend to special connectors such as the connector H, Fig. 6. Owing to the absence of ringing equipment and the usual battery supply bridges the circuit of the connector H is very simple. The banks of the special toll connectors are multipled straight with the banks of the local connectors. In other words, each group of lines in the branch exchange is accessible through a certain number of connectors such as the connector H, and also through a certain number of connectors such as the connector H, the banks of all the connectors being multipled as shown, in the case of the connectors mentioned, at the right hand end of Fig. 6.

At the top of Fig. 4 and just above the key circuit equipment M there is shown the attendant operators head set, indicated by the reference character Opr. The only feature of this equipment which needs special mention is the relay 370 which is provided to shift from single wire to loop calling; To explain this a little more fully, the calling device S is adapted upon the operation of key K to be included in a ground return control circuit of the selector E; while when the key K is actuated a bridge is closed across the trunk conductors which includes the calling device, the relay 370 being energized to produce the necessary circuit changes. It will be clear of course that the operators equipment Opr is common to a plurality of key circuit equipments such as the equipment M, and to a plurality of key circuit equipments such as the equipment N.

For the purpose of supplying current for operating and talking purposes have shown throughout the drawings a plurality of batteries, but it is to be understood that there is preferably but one battery for each exchange. each battery having its positive pole grounded. 1n order not to encumber the drawing? reference characters have been omitted from the separate batteries therein shown, and to avoid any confusion on this account it is noted that when in the specification a circuit is traced to battery, it extends to the ungrounded or live pole of the common exchange battery. The reference characters 1R, IR, and IR indicate intermittent ringing machines of which there is preferably one in each exchange. Similarly, each exchange is provided with a busy signaling machine of the usual type which are shown at several places in the drawings and indicated by the reference characters ex ea -W- Having described briefly the general layout of the system and the character of the apparatus involved, I will now proceed to explain in a more detailed manner the operation of the circuits. For this purpose it will be assumed that the toll operator having the cord circuit 0, Fig. 1, desires to connect the toll line 23 with the line of the private branch exchange substation A, Fig. 4, this being the complete circuit connection shown in the drawings. Afterward a number of other connections will be briefly described in order to completely illustrate the different features of the invention.

To proceed with the establishment of the eminection, the toll operator, after first observing that the toll service trunk with which the lamp L is associated is idle, as icatcd by the unlightcd condit on of the said lamp, will insert the calling plug of the cord circuit 0 in the jack J of the service trunk. By the insertion of the plug in the jack a control circuit is completed for the line relay 50 of the toll first selector V, Fig. 2, over the following path: ground at winding of supervisory relay 9, contacts of the calling device K sleeve of the plug, sleeve of jack J, contactspring 1.5, conductor i6, armature 81 and its resting contact, and the winding of the line relay 50 to battery. Upon the closure of the above circuit relays 9 and 50 are energized in series, the former relay closing a circuit for the supervisory lamp L in an obvious manner. Relay 50, upon energizing, closes a circuit for the slow acting release relay 51 which relay upon energizing in turn prepares a circuit for the vertical magnet 57 in the usual manner, and also closes acircuit for the busy lamp L and its multiples at other operators positions over the following path: ground at G, armature 82 and its working contact, conductor 17, and the busy lamp L to battery. By the illumination of the busy lamps the other operators are warned that the service trunk has been taken for use.

The foregoing operations have occurred in response to the insertion of the plug in the jack. The operator may now proceed to dial the number of the desired subscriber in the private branch exchange, but before so doing she is required first to operate the calling rlcvice key K the actuation of which key resul in the substitution of the. calling for the supervisory relay 9 in the device circuit ot the line relay ill of the selector V. YVhen now the calling device is actuated in accordance with the first digit of the quired number, a sei' of interruptions is produced in the circuu at the line relay 50. llesuonsire to these into iptions of its circuit, the line relay is decnergizcd a corresponding; number of times and at each do energizalion sends an impulse to the vertical magnet over the following path: ground at it, armature 83 and its resting contact, resting contact of armature 84L and the said armature, winding of low resista .cc relay 32, armature 85 and its working contact, and the winding of the vertical magnet 51'" to battery. in response to these-impulses the vertical ma 1' 1s actuated to raise the switch shah st p-by-step until the wipers 6? to (33, inclusive, arrive at thehoriznmtal level ol bank contacts in which are terminatc il trunk lines extending to the required group of toll second selectors. The relay 52 is energized in series with the vertical magnet and being slow acting retains its armature attracted during the series of impulses. lily the miergization of relay an initial energizing circuit is completed for relay 53 as follows: grounded conductor 17, armature 86, spring 87, vinding of relay 53, and the interrupter contact of the rotary magnet 56 to battery. the upward,movement of? the shal the elf-normal springs 58 are pcrmltlaul to close, whereby the relay 53, ring, is enabled to complete a it for itself-as follows: ground- "cnzl n 17, working contact of armature 8H and the said armature, ofhnormal.

, winding of relay 53, and the interrupter contact of the rotary magnet56 to battery. a further result of the energization of relay 53 circuit is prepared for the rot y magnet 56 which, however, is held open during the vertical movement of the switch by the slow acting relay 52. lt this point it should be mentioned that soon as he off-horn a1 springs 58 are clos d, the line switching relay 54- is connected in scr with the relay 53 orer the following path: grounded conductor 17, winding of the rel y 54:, oil-normal spri. winding of relay an; the interrupter contact of the rotary mas ict to batter lit is to be not" lmwmer, that the above circuit has already been groumlcd at a point 21',- way between the two relays; whence it tollows hat the relay is short circuited and remains inoperative for the present.

At the end of the series of impulses the show acting relay 52 deeinergizes and completes the circuit of the rotary magnet 56 as follows: grounded conductor 17, working springs;

contact of armature 88 and the said armature, off-normal springs 58, spring 87 and the contact normally engaged thereby, winding of rotary magnet 56, and. interrupter contactsolf the said magnet to battery. The rotary magnet is energized over the above circuit and rotates the switch shaft one step, thereby bringing the wipers co to 63, inclusive, into engagement with the first set of.

new point, and the rotary magnet again closing its interrupter contact. The operation now depends upon whether or not the first trunk line 1s busy. If tlns trunk line is busy, the test contact with. which the test wiper 61 is in engagement will have a ground potential upon it, and a circuit will be established by way of the test wiper and the armature 89 of relay 54 which is ellective to maintain relay 54.: short circuited and to again energize the relay 53. When the first trunk line is busy, then, the relay 53 will again attract its armature to again close the circuit of the rotary magnet 56, resulting in the advance of the switch wipers another step. It will be seen then, that the relay 53 will operate as an impulse sender or a stepping relay to advance the switch wipers step-by-step through the medium of the rotary magnet, as long as the test wiper con-' tinues to engage grounded or busy test contacts. As soon as the first ungroundetd test contact is reached, assumed to be the test con tact 65, and the rotary magnet 56 decnergizes to close its interrupter contact, the relay 54: will no longer be short circuited, but will instantly energize in series with the relay 53 over the, circuit previously traced. Relay 5 1- is of such high resistance that relay 58 remains inoperative. Upon energizing, relay 5 1 opens the circuit of the release magnet 55 at its armature 8d; at its armature 89 shifts the connection from the test wiper 61 from its lower to its upper terminal; and at its upper armature 81, disconnects the conductor 16 from the line relay 50 and extends it instead to the line relay 100 of toll second second selector W as follows: conductor 16, armature 81 and its working contact, wiper 62, bank contact 66, armature 123 and its 7 G,'working contact of armature 125 and the said armature, conductor 70, bank contact 65, wiper 61, and armature 89 and its working contact to conductor 17, where it joins the previously described circuit of the busy lamps, such as the lamp L Fig. 1. A branch of the above circuit serves to maintain the switching relay 54 energized over the previously traced circuit, including the relay 53. Although the relays and 51 of the selector V are denergized immediately following the energization of relay 54, owing to the fact that the latter relay is slow acting, ground G is not disconnected from conductor 17 until after the holding circuit extending back from ground G is completed. Ground G also extends by way of a branch conductor 70 to the test contact 72 and its multiples in the banks of the toll selector repeaters having access to the toll second selector W, where by a ground potential on these test contacts said selector is made busy.

The operator may .now proceed to manipulate her calling device in accordance with the second digit of the number, thereby producing a series of interruptions in the circuit of the line relay 100 of the toll second selector W. In response to these interruptions of its circuit the line relay 100 dee er,- gizes a number of times and at each deenergzation transmits an impulse from ground 6 to the vertical magnet 107 over the following path: ground at G, armature 121. and its resting contact, resting contact of armature 118 and the said armature, armature 126 and its working contact, winding of relay 102, and the winding of the vertical magnet 107 to battery. The vertical magnet 107 is accordingly actuated raising the switch shaft step by step until the wipers 150 to 154, inclusive, arrive at the horizontal level of bank contacts in which are-,terminated trunk lines extending to the private branch exchange repeaters, such as the repeater F. The relay 102 is energized in series with the vertical magnet, and being slow acting, it retains its arn'iature during the series of impulses. At the first upward movement ofithe shaft the off-normal springs 108 are permitted to close, thereby completing an initial energizing circuit for the re lay 103 as follows: ground at G, working contacts of armature 125, armature 127 and its working contact, off-normal springs 108 and the winding of relay 103 to battery. Upon energizing, the relay 103 closes a loclring circuit for itself as follows: grounded conductor 70, right hand interrupter contact of the rotary magnet 105, working contact of armature 129 and the said armature, off-normal springs 108, and the winding of the said relay 103 to battery. As a further result of its energization relay 103 prepares a circuit for the rotary magnet 105 which,

however, is held open during the vertical movement of the switch by the slow acting relay 102. As in the case of the toll first select-or, the line switching relay, or the relay 110, and the stepping relay, or the relay 103, of the toll second selector, are connected in series upon the initial upward movement of the switch shaft; and as this circuit in the second selector is slightly different from the one already traced in the first selector, it will be advisable to point out the path traversed: grounded conductor 70. winding of relay 110, left hand interrupter contact of the rotary magnet 105, off-normal springs 108, and the winding of relay 103 to battery. Ground G being connected to the above circuit at the junction of the two relays, relay 110 is short-circuited and in operative for the present. At the end of the series of impulses the slow acting relay 102 deenergizes and completes the rotary magnet circuit, which may be traced as follows: ground at G working contacts of armature 125, armature 127 and its resting contact, working contact of armature 128 and the said armature, and the winding of the rotary magnet 105 to battery. The rotary magnet 105 is energized over he above circuit and rotates the switch shaft one step,

thereby advancing the wipers 150 to 154.

inclusive, into engagement with the first set of contacts in the level opposite which they were raised. Near the end of its stroke the rotary magnet opens both its interrupter contacts, thereby opening the circuit connecting the relays 110 and 103 and also breaking the locking circuit of the'latter re lay. Relay 103 therefore is deeuergized and breaks the circuit of the rotary magnet which deenergizes in turn and again closes its interrupter contacts. The operation now depends upon whether or not the first trunk line is busy. If there is a ground potential upon the test contact with which the wiper 151 is now in engagement, a circuit will be established which will. be effective to maintain the relay 110 short circuited and to again energize the relay 103. This circuit may be traced as follows: ground on busy test contact, test wiper 151, armature 130 and its resting contact, armature 114 and its resting contact, left hand interrupter contact of the rotary magnet 105, off normal. springs 108, and the winding of relay 103 to battery. It follows that if the first trunk line is busy relay 103 will again energize to close the circuit of the rotary magnet 105. resulting in the advance of the switch wipers another step. It will be seen from the foregoing that the operation of the second selector WV in selecting an idle trunk line is similar to the previously described opera tion of the first selector V in like case, the shaft being rotated step by step through the conjoint action of the relay 103 and the rotary'inagnet 105 as long as the test wiper 151 continues to engage grounded or busy test contacts. As soon as the first ungrounded test contact is reached, assumed to be the test contact 156, and the rotary magnet 105 deenergizes to close its interrupter contacts, relay 110 will no longer be short circuited but will at once energize in series with the relay 103 over the circuit previously traced. Owing to the high resistance of relay 1.10, relay 103 remains inoperative. Upon energizing, relay 110 opens a contact in the circuit of the release magnet 106 at its armature 118 in order to guard against the release of the switch upon deenergization of relays 100 and 101; disconnects the test wiper 151 from its own upper terminal at its armature 11 1 and connects it instead to the resistance 122; at its armatures 11.5 and 116 connects the repeating coil windings .112 and 113 with the upper and lower windings, respectively, of the relay 109; and at its armature 117 completes a control circuit extending to the repeater F, Fig. 3, over a path which may be traced as follows:

ground at G, armature 121 and its working contact, worlnng contact 01' armature 117 and the said armature, resistance 170, wiper 153, bank contact 158, conductor 163, upper contacts of the back bridge or reversing relay 200, and the upper winding of the line relay 201 to battery. Line relay 201 is energized upon the closure of the above circuit and completes at its armature 212 a circuit for the slow acting release relay202. The energization of relay 202 is followed by a number of important results which will be described in detail. First to be considered is the grounding of conductor 166 at the upper armature 213 of the said relay 202, whereby ground G is extended by way or" the said conductor 166 to the test contact 168 and its multiples in the banks 01 the local second selectors having access to the repeater 13, thus rendering the repeater 1* busy to these selectors. Ground G also extends to the test contact 156 and its multiples in the banks oi. the other toll second selectors over the following path: ground G working contact of armature 213 and the said armature, conductor 166, winding of the low resistance relay 203, and the con ductor 161 to the test contact 156. The relay 203 being of low resistance, test contact 156 and its multiples are brought suiliciently near to ground potential to render the re peater l busy to the toll second selectors also. 11. continuation of the circuit last traced extends by way of the test wiper 151 of the second selector 1V, armature 130 and its resting contact, armature 11d and its working contact, and the resistance 122 to battery. Relay 203 is accordingly energized to open a contact in the circuit of relay 205 and with other results which will appear ductors 236 and 238 are disconnected from their normal battery and ground connections in the line switch C. Still another result of the energization of the-relay is the closure of a circuit for the relay 208 over the following path: ground at G, working contacts of armature 213, armature 223 and its resting contact, and the winding of relay 208 to battery. The relays 203 and 208 being new energized, it will be seen that the incoming line conductors 160 and 161 are extended by a direct metallic connection through the repeater to the trunk conductors 233 and 235, respectively.

By the energization of relay 208 a control circuit extending to the incoming selector at the branch exchange is closed as follows: ground at G armature 229 and its working contact, resistance 209, conductor 234;, contact springs 328 and 321' of key K at the attendant operators position, Fig. 41-, con tact springs 315 and 316 out key 15 conductor 382, armature'dlQ of relay 104: of the selector E, Fig. 5, and its resting contact, and the winding of the line relay 400 to battery. The line relay 400 is energized upon the closure of the above circuit and completes the usual energizing circuit for the slow acting release relay 101. By the energization of the latter relay the circuit of the vertical magnet 411 is prepared in the usual manner, and at the same time ground G is connected to the conductor 383. A circuit for the busy lamp L at the attendant operators position may now be traced as follows: ground G working contact of armature 109 and the said armature, conductor 383, contact springs 31'? and 318 of key iiiconductor 386 and the busy lamp L to bat tery. The illumination of the busy lamp L indicates to the attendant operator'that the trunk line associated therewith has been taken for use. cuit extends by way of conductor 386 to the test contact 752 and its multiples in the banks of local first selectors, including the selector E, where by ground potential on these test contacts the trunk line under consideration is made busy to outgoing calls from the branch exchange.

To summarize briefly the operations that have taken place so far, the toll operator at the main exchange by dialing the first two digits of the number has operated the toll first selector V and the toll second selector 1V, to extend the connection by -way oi? the repeater F and the trunk line associated A branch of the above cirtherewith to the incoming selector E at the branch exchange; and by the operation of the relays 400 and 401 of the incoming se lector a busy signal at the attendants position has been lighted and the trunk line in use has been made busy to the local first selectors at the private branch exclmnge.

The toll operator may now proceed to dial the digits which are to control the in coming selector E and the connector ll. Fig. 6, to complete the required connection. By the operation of the calling device in accordance with the next digit called a series of interruptions is produced in the cir cuit of the line relay 100 of the selector il as before. The line relay is accordingly deenergized a number of times, and at each deenergization interrupts the circuit of the line relay 201 of the repeater F, Fig. 3. Res sponsive to these interruptions of its circuit, the line relay 201 is also dei nergized a number of times to repeat the interruptions into the circuit of the line relay 400 of the incoming selector I), Fig. 5. It follows that the relay 400 will be deenergized a number of times corresponding to the digit called, and will transmit at each deenergization an impulse to the vertical magnet 411 over the following circuit: ground at G, armature 408 and its resting contact, resting contact of armature 423 and the said armature, armature 410 and its working contact, winding of relay 402, and the winding of the vertical magnet 411 to battery. In response to these impulses. the vertical magnet 411 is actuated to raise the switch shaft step'by step until the wipers 440 to 443, inclusive, arrive at the: horizontal level of bank contacts which are terminals of trunk lines extending to the required group of toll connector switches. The relay 402 which is included in the vertical magnet circuit is slow acting and retains its armatures attracted during the series of impulses. At the first upward movement of the shaft the off-normal. springs 467 and 464 are permitted to close, thereby completing an initial energizing circuit for the stepping relay 403 follows: grounded conductor 3S3, armature 414 and its working contact, off-normal springs 407 and 464, winding of relay 403, conductor 38?, contact springs 334 and 3830f key K and contact springs 313 and 512 of the call through key K to battery. (It is to be noted that the call through key K" is assumed to be in operated position. The function of this key in blocking calls will be explained fully later on, and it will be sufficient for the present to call attention to the fact that the relay 403 of the selector E is supplied with battery through the contacts of this key.) Upon en rgizing, relay 403 completes a locking circuit for itself as follows: ground at G, working contact of armature 417 and the said armature, interrupter contact of the rotary magnet 412, off-normal springs 67 and 464, winding of the said relay 403, conductor 38?, contact springs and 333 of key K and contact springs 313 and 312 of key K" to battery. At its upper armature 416 relay 40 prepares a circuit for the rotary magnet 412 which is held open during the operation of the vertical magnet by the slow acting relay 402. The usual circuit connecting the switching relay 404 and the stepping relay 4.03 in series nay be traced as follows: grounded conductor 38%, rotary off-normal springs 471 and 470, winding of relay 404, interrupter contact of the rotary magnet 412, off-normal. spring and 404, winding of relay 403, conductor 387, and thence over the path previously traced to battery by way of the call, through key K". This circuit being grounded at the junction of the two relays, as previously explained, relay 404 is shortcircuited and remains deenergized for the present. fit the end of the series of impulses which control the vertical operation of the switch, the slow acting relay 402 retracts its armatures, thereby completing a circuit for the rotary magnet 412 as follows: groun ed conductor 383, armature 414 and 'es ng contact, working contact of armature and the said armature, and the winding of the rotary magnet 412 to battery. Upon closure of its circuit the rotary magnet i energized. to advance the wipers 1 inclusive, into engagement with i set of contacts in the level opposite ney were raised. Near the end of its e rotary magnet breaks the locking circuit of relay 403 which relay is accord l deencrgized to break the circuit of the rotary magnet, which also deenergizes. The operation of selecting an idle trunk line which now takes place is similar to the corresponding operations already described in the case of toll selectors V and W, and need not be described in detail. It will be suflicient to say that as long as the test wiper 442 of the selector engages busy or grounded test contacts, the switch shaft will continue to be rotated by the cooperative ac tion of the stepping relay 403 and the rotary magnet 412, the relay 404, meanwhile, being short-circuited and inoperative. When the test wiper 442 arrives at the first ungrounded test contact, assumed to be the test contact 446, and the rotarymagnet 412 retracts its armature, the relay 404 will instantly energize in series with. the relay 403 over the circuit previously traced, the latter relay re maining inoperative owing to the high re- 'sisencc of relay 404. Upon energizing, re-

lay 404 opens a contact in the circuit of the release magnet 41.3 at its armature 423 in or -1 i ft} T' i nor to P13. cnt t 10 release 0. 1e sn i on upon de'c ergization oit relays 400 and 401; shifts test wiper 442 from its own upper terminal to its lower terminal at armature 418; connects the lower terminal of winding of relay 403 to the resistance 450 at its armature 421, for a purpose to be described later; at its armatures 420 and 422 connects up the line wipers 440 and 443; and at its arma ture 410 disconnects the operating conduc tor 362 from the line relay 400 and connects it instead to the line relay 500 of the connector ll. over the following path: conductor 382, armature. 419 and its working contact, wiper bank contact 445, and the line relay 500 to battery. Following the closure of the above circuit the line relay 500 is encrgized to close the usual circuit for the slow acting release relay 501. This latter relay, upon energizing, prepares the usual circuit for the vertical and rotary magnets 506 and 507, and also connects the ground GM to the conductor 383 as a substitutefor ground G which is removed upon the deenergization of relays 400 and 401. This substitute ground connection or holding circuit is established as follows: ground at working contact of armature and the said armature, conductor 461, bank contact 446, wiper 442, and armature 418 and its working contact to the conductor It is understood that since the relay 401 is slow acting it does not deenergiae until a" ter the ground connection above described has been established.

Before proceeding with the operation of the connector H it will be necessary to return to the incoming selector E and note a number of circuits, which it was not convenient to describe before. When the slow acting relay 4 2 energizes at the beginning of the vertical movement of the selector, a circuit is completed for the ring cut-off relay 406 as follows: ground at G, resistance 399, contact springs 337 and 336 of key K con- 'ductor 388, armature 415 and its working contact, and the upper winding of relay 406 to battery. Upon energizing, relay 406 establishes a locking circuit for itself as follows: ground at G, ofl:'-normal springs 463 and 466, (closed at the first upward movement of the shaft) working contact of armature 428 and the said armature, and the upper winding of the said relay 406 to battery. As a further result of its energization relay 406 disconnects its own lower winding and also a lead extending from the ringing machine IR, and also closes several contacts in the talking circuit. hen the otf norinal springs 463 and466 are closed a circuit is completed for the supervisory lamp if at the-attendant operators position, the circuit being traceable as follows: ground at G, off-normal springs 463 and 466, armature 426 and its resting contact, conductor 381, supervisory lamp H, and thearinature 310 and its resting contact to battery. The supervisory lamp thus lighted will be extinguished when the connection is completed and the called subscriber answers. It will be advisable also at this time to explain the purpose of the rotary off-normal springs 470 to 472, inclusive. In case all the trunk lines of the selector level are busy, the selector will of course not stop on any of these trunk lines, but will continueto rotate until at the eleventh step a cam'on the shaft actuates the rotary off-normal springs, springs 470 and 471 being separated and springs 472 and 473 being closed. At the eleventh step the test wiper 442 will have been rotated past the last test contact in the level, as a result of which operation the relay 403 will not be able to energize again to cause further advance of the switch. Switching relay 404, however, is not energized because of its circuit being open at the rotary off-normal springs 470 and 471. By the engagement of springs 472 and 473 a lead from the busy signaling machine Q is connected by way of the resistance 469 and the tenth level off-normal springs 460 and 461 to the lower heavy line conductor 389, whereby the toll operator at the distant exchange is given the busy signal. The busy signaling machine Q, preferably produces a tone different in character from the tone used to indicate the busycondition of a called subscribers line so that the toll operatoris able to distinguish between the two. Being informed by the appearance on the line of this distinctive busy test, the operator will know that the connection can not be completed for lack of trunking capacity at the branch exchange and will immediately .(lisconnect. These operations have been mentioned but briefly at this time, but they will be understood fully before thespecification is completed. Returning to the connector .H,

Fig. 6, when the operator dials the next digit of the number, a series of interruptions are produced in the circuit of the line relay 500, being repeated by the relays of the selector WV and 201 of the repeater F. Responsive to these interruptions of its circuit the line relay 500 is denergized a number of times and sends at each deenergization an impulse to the vertical magnet 506 over the following path: ground at G", armature 512 and its resting contact, armature 514 and its working contact, winding of relay ,magnet, and being slow acting, retains its armature attracted during the vertical ovementpf the switch to close a circuit for the private magnet 509. At the end of the series of impulses the relay 503 and the private magnet denergize. The latter controls the side switch wipers 510 and 511 in the usual manner and advance them to their second position.

The toll operator may now call the final digit in the number of substation A. As before, a series of interruptions are produced in the circuit of the line relay 500, resulting in another series of de'energizations of the said relay. Now, however, the side switch wiper 510 being in its second position, the line relay 500 transmits a series of impulses to the rotary magnet 507 which is accordingly operated to rotate the wipers 540, 541 and 542 until they come to rest in engagement with bank contacts 543, 544 and 545, respectively. The slow acting relay 503 and the private magnet 509 are energized asbefore during the last series of impulses, and upon decnergizing, the private magnet advances the side switch wipers 510 and 511 to their third position (it being assumed that the called line is idle). It should be noted that when the private magnet 509 is energized, a circuit is closed for the slow acting relay 504. During the rotation of the switch the two slow acting relays 503 and 504 serve to disconnect the incoming line conductors 460 and 463 from the line wipers 540 and 542, respectively. As soon as the side switch wiper 511 comes into engagement with its third position contact point a circuit is established for the cut-off winding of the. line switch as follows: ground at G", side switch wiper 511 in third position, test wiper 541, test contact 544, conductor 547, and the cut-off winding 656 to battery. By the energization' of the cut-ofl winding 656, the cut-off armature 658 is operated to disconnect the line conductors of substations A from their normal battery and ground connections in line switch C. Ground G also extends to multiples of test contact 544 in the banks of the other toll connectors of the group, and likewise to test contact 844 and its multiples in the banks of local connectors, such as the connector H, thereby making the line of substation A busy to other calls.

When the side switch wiper 511 goes to third position, it also closes, in conjunction with the side switch wiper 510, a circuit for the relay 505 which may be traced as follows: ground at G, side switch wiper 511' in third position, winding of relay 505, and the side switch wiper 510 in third position to battery. It has been stated before, that the relay 504 is energized during the rotation of the switch, its circuit being closed by the private magnet, and since this relay 504 is slow acting, it remains in operated positron for an instant after the relay 505 energizes- Du-ring the brief interval that these two relays 504 and 505 are both in operated position the busy signaling machine Q is connected to the upper line conductor 460, and a circuit is closed for the wiper switclr ing relay 407 of the selector E as follows: ground at G, lower winding of relay 407, armature 420 and its working contact, resting contact of armature 431 and the said armature, wiper 440, bank contact 444, conductor 460, armature 517 and its working contact, working contact of armature 518 and the said armature, and the secondary winding of the busy signaling machine induction coil, to battery. Upon energizing, relay 407 establishes a locking circuit for itself as follows: ground at G, off-normal springs 463 and 466, working contact of armature 432 and the said armature, and the upper winding of the said relay 407 to battery. As a further result of its energization relay 407 connects the line wiper 440 with the condenser 434 and the upper winding of the relay 405 at its armature 431, and at its armature 433 connects the line wiper 443 with the condenser 435, and with the lower winding of the relay 405. The circuits through these armatures 431 and 433 will be traced in detail hereafter.

The toll operator at the main exchange has now completed the required connection. and she will therefore restore her calling evice key K to its normal position. By this operation the SIIIQGIVlSfH) relay 9 replaces the calling device S in the circuit of the line relay 100 of the selector V7, and encrgizerl to again light the supervisory lamp L. The next operation is the signaling of the called subscriber which takes place as follows: When the operator throws her ringing key K alternating current is projected out over the heavy trunk conductors to the toll second selector W, Where it actuates the bridged alternating current relay 111. Upon energizing, the relay 1.11 closes a circuit for the slow acting relay 104 as follows: ground at G contact and armature of said relay 111, and the winding of relay 104 to battery. Relay 104 is accordingly energized, and at its upper armature 130 breaks the circuit of relay 203 the repeater thus permitting it to deenergize. At the same time at its lower armature 131'. relay 104 closes a circuit for the ringing relay 204 of the repeater F as follows: ground at (1, working mntact of armature 131 and the said armature, wiper 152, bank contact 157, conductor 162, and the winding of relay 204, to battery. By the deenergization of relay 203 and the energization of relay 204, a signaling circuit, including the line of substation A, is completed as follows: ground at G generator Gen, working contact of armature 219 and the said armature, resting contact of armature 221 and the said armature, resting contact of armzu ture 217 and the said armature, resting conof the rolled subscriber.

tact of armature 228 and thesaid armature, working contact of armature 231 and the said armature, trunk conductor 235, contact springs 369 and 36S. and contact springs 36 1 and 365 of key K contact springs 330 and of key K contact springs 353 and of key K conductor 089, working con tact of armature 480 and the said armature, condenser 185, left hand working contact of armature and the said armature, wiper as, bank contact 4427, conductor 463, armature i. and its resting contact, resting contact oil armature 516 and the said armature, wiper M2, bank contact 5415, normal condnctor 5e18, conductor 653, contact springs 6'72 and 671 of key K contact springs .645

and (i41 ot key K contact springs 615 and tact, condenser 43 1, conductor 380, contact springs 351 and 352 of key K contact springs 325 and 326 of key K contactsnrings R61 and 360, and contact springs 367 and 366? of key K, trunk conductor 233, armature 230 and its working contact, arnmture i326 and its resting contact, armature 215 and its resting contact, armature and its working contact, resistance 298. and through the battery to ground G. T he above circuit is, closed as long as the toll operator holds her ringing}; key K in oper ated position, and ringing current trom the generator {ten operates the ringer 605 at the called substation A. to signal-the sub: scriber. lit is to be observed that at the selector it. the relay 105 is connected in brid oi the circuit in series, with the battery in readiness to be operated uponthe response The windings of relay 405 are preferably oi rather high resistance. and the relay is given a stiff a.d just-merit so that it does not respond. to the rlneinn' current. l .Vlirm the snbscriliier at substation A removes his receiver in response to the call, a circuit is-closed for the relay 105 at the so ll as follows: ground at G lower o't relay 1,05, workino; contact of 9 and the said armature. right mg contact of. armature 133 and. armature. wiper 14:3, thence over pr viously traced circuit to substation r. t ili r lfi'li the transmitter 603, receiver the upper switch hook contacts at l substation, and back over the path already traced through the wiper 4410, from w iich point the circuit continues by way of armature 4:31 and its right hand working cont-act, armature and its working contact, and the upper winding of relay 4105 to battery. The energization of relay 05 responsive of the removal of the receiver has a number of important results. First to be mentioned is the opening of the circuit of the supervisory lamp L at armature 4265, thereby extinguishing the said lamp to notify the attendant operator that the call has been answered. At the same time a circuit is closedfor the relay 304: at the attendant operators position as follows:

ground at G, oft-normal springs 163 and- 466, armature 4126 and its working contact, conductor 384:, contact springs 34.11 and 3&0 of key K and the winding of relay 1- to battery. Upon energizing, relay 30 i establishes a locking circuit for itself as follows: ground at G, working contact of armature 409 and the said armature, con

ductor 383, contact springs 317 and 318 of key K armature 311 and its working contact, contact springs 34:1 and 340 otkey K and the winding of the said relay to battery. At its upper armature 810, relay 304: shifts the circuit of the supervisory lamp L from its direct battery connection. to battery through the night alarm signal for a purpose to be described hereafter. further result of the energization of relay 105 is the short circuitino; of condensers 134: and 41-35. at armatures 42 1 and 4:25, respectively. By this operation a direct metallic connection is established trom the toll second sel ctor W through the repeater F, the key circuit equipment M, the incoming; selector E, and the connector H to the nor-- mal conductors ot the called substation A... thereby per. ittine the battery supplv lay 109 at the selector W to be ener 'zed over the followingr'pathr ground at Q". lower winding; of relay 109, working conta of armature 116 and the said arrnatni-t'e: posting coil winding 11- wiper 154'. bank contact 159, conductor 164, work 0'? armature 521.7. and the said arrna.

ing contact of armature and the said armature, and the working cont-act ot ture and the said armature to trunk conductor thence throw a. the key circuit equipn'ient M aspreviously traced, to conductor and, thence bv way of armor tu're of relay 4% and its working con- 4.!! ta worlrin contact ot armature 4:99 and. the said or. re. and the ran-ht hand worlr- .Lc, as,

the circuit continues to and. thron h subst tion A and be oh to wiper 40 ove a path previously pointed ou t. c by way of armature 4:31 and its working. contact, armature and its working contact, working contact of armature 424 of relay 405 and the said armature, line conductor 380, thence through the key circuit equipment M as previously traced, to trunk conductor 93?), and them-e by way of armature 230 and its working contact, armature 226 and its resting contact armature 215 and its working contact, conductor 160, bank contact 155, wiper 150, repeating coil winding 112. armature 115 and its working contact, and the upper winding of relay 109 to battery.

The energization of relay 109 has the following results: At armature 120 the alternating current relay 111 is disconnected from in bridge of the line conductors; at arn'iature 119 the left hand windings of the repeating coil are connected to complete the talking circuit; at armature 171 ground is connected to the control circuit 01 the line relay 201 of the repeater F as a substitute for ground G. removed an instant later by the decnergization of line relay 100, as will appear shortly; and at armature 12 i conductor 71 is disconnected from. the winding of relay 100 and is connected instead to the winding of? relay 101. It should be mentioned at this point, that the line relay 100 is of moderate resistance. preferably 250 ohms, while the resistance ot the release relay 101 should be at least 1300 ohms. The supervisory relay at the cord circuit 0 is marginally adjusted so that it will energize in series with the line relay 100 and deinergize when in series with r the release relay 101 It will be seen then that when the relay 109 energizes following the removal of the receiver at the called substation and the resulting energization of relay 405, the resistance of the circuit including the supervisory relay 9 at the cord cir cuit will be sufficiently increased to cause the dei nergization of the said relay. The supervisory lamp L is thus extinguished to notify the toll operator that the called subscriber has answered the telephone.

By the foregoing operations the toll operator has extended the connection to the line of the called subscriber at substation A. The connection to the calling line, presurnably connected to the toll line 23 at the distant end thereof, is accomplished by inserting the answering plug of the cord circuit O in the jack J after which the two connected subscribers may converse as desired. The called substation A is supplied with talking current through the winding of relay 405 of the selector E at the branch exchange, and the windings of relay 109 of the selector V at the main exchange in multiple; while the other substation may be supplied with talking current from connective apparatus associated therewith during conversation in any suitableor desired manner. lt-is to be observed that the connection shown includes but a single inductive connection, the repeating coil at the toll selector 1V,- and with this one exception is direct metallic throughout. There is. moreover, minimum of bridges across the talking circuit, when all its complexities are considered, resulting in the most ellicient transmission possible under the circumstances.

lVhen the conversation is finished the subscribers will replace their receivers. The hanging up of the receiver at substation A brings about the deiinergization of relays 105 of the selector E and 109 of the toll selector 1V. By the deenergization of the former relay, and owing to the fact that the relay 30% at the attendants switchboard is locked up, the circuit of the supervisory lamp L is now com )leted by way of the night alarm signal NJ. and the attendant thus given both a visual and an audible disconnect signal. At the same time, by the de energization of the relay 109 at the main exchange the line relay 100 is again inserted in the circuit of the supervisory relay 9 at the cord circuit 0, and the latter relay is energized to cause the illumination of the lamp L. The lighting of the supervisory lamp L of course gives the toll operator a disconnect signal. It may happen that the toll operator wishes to talk to the attendant at the private branch exchange concerning the charge for the conversation just finished, or some other matter, in which case she has simply to wait on the line until the attendant responds to the ringing of her night alarm; but ordinarily the toll operator will immediately disconnect the local connection by withdrawing the calling plug of the cord circuit from the jack. Being familiar with these facts, the attendant need not respond except to a prolonged signal.

lVhen the plug is withdrawn from jack J the circuit of the line relay 100 of the toll selector WV is broken. The consequent decnergization of the line relay is followed by the denergization of the release relay 101, and results also in the breaking of the control circuit including the line relay 201 ofthe repeater F. By the former operation ground G is disconnected from the holding circuit extending back to the selector V, and also the line switching relay 1.1.0 is permitted to deenergiz e. At the same time a circuit is closed for the release magnet 106 of the selector W as follows: ground at G", armature 121 and its resting contact, resting contact of armature 118 and the said armature, armature 126 and its resting contact, the off-normal springs 108'. and the winding of release magnet 106 to battery. By the energization of the release magnet the selector W is restored to normal position in the usual and well understood manner, the release magnet circuit being opened at the offnormal springs when the shaft reaches its lowermost position. At the selector V the removal of ground G from conductor 17 results in the deenergization of the line switching relay 54c and the extinguishing of the busy lamps at the toll operators positions. The definergization of relay 54: results in the closure of the circuit of the release magnet 55 and the selector V is accordingly restored to normal position substantially as was described in the case of selector W.

*hcu the circuit of the line relay 201 of the repeater F is broken and the line relay deenergizes, the release relay 202 deenergizes and also the control circuit extending to the line relay 500 of the connector H at the branch exchange is broken. Following the dciinergization oi? relay 202, the relays of the repeater which were being energized from ground G and also the cut-cit armature of line switch 0, are permitted to fall back, and at the same time ground is removed from the test contacts in the banks or the selector switches having access to the repeater.

When the line relay 500 of the connector H at the branch exchange deenergizes, it re sults in the deenergization of the release relay 501. and the breaking of the holding circuit extending back to the selector E via conductor Q61. The connector H is restored to normal upon the deenergization of its line and release relays through the medium of release magnet 508. At the selector E, upon the removal of the holding ground supplied from connector H, the line switching relay 404: is deenergized and closes the usual circuit for the release magnet 4213, whereupon the selector switch is restored to normal. A the shaft of the selector reaches its lowest position the locking circuits oi relays &06 and 4:07 are broken and these relays deenergize. At the attendants position the busy lamp L is extinguished and the relay 304: is unlocked and deenergized by the removal of ground from conductor 2383 which during the connection was joined to conductor 461 extending to the connector H.

.i't will be seen then that when the toll operator at the main exchange removes the plug irom jack J all the apparatus, including that at the branch exchange is released and restored to normal position. The foregoing description-of the releasing operations is rather brief, but there is nothing new or unusual in these operations, and when it is remembered that the various circuits are in general broken in the inverse order to that in which they were established, it is believed that no diiiiculty will be experienced in understa o ding them.

It will now be assumed thatthe subscriber at substation 21, when called by the toll op erator at the main exchange as described in the twrgoing, was engaged in conversation;

and the operations under these circumstances will be briefly described. When the line of sul :-:-:tar m is b=usytliere will be a ground potential upon the tst contact 544 in the bank of the connector and this being the case, when the slow acting relay 503 de'elnergizes at the end of the final series of operatmg impulses, the private'magnet 509 does not deenergize but held up over the following test circuit: ground on busy test contact wiper 5&1, side switch wiper 511 in second position, winding of test relay 502, contact 531, spring 532, and the winding of the said private magnet to battery. Since the private magnet is maintained energized the side switch. wipers areheld in second position, the relay 505 is not energized, and consequently no momentary impulse is transmitted back over conductor 460 to the wiper switching relay i0? of the selector E. The

relay 407 therefore does not energize when the connector Pl lands on a busy line. Instead, at the connector H, the test relay 502 is energized in series with the private magnet and connects the busy signaling machine Q with the lower line conductor 463. Now since the relay L0?" at the selector E is not energized the condenser 435 is not included in the lower line circuit and current will flow through the lower winding of relay 109 at the toll secondselector at the main exchange over a path which may be briefly traced as follows: ground at G, lower winding of rela 109, working contact of armature 116 and the said armature, repeating coil winding 113, wiper 15 i, bank'contact 159, conductor 164, relay contacts of repeater i trunk conductor 285, key contacts of key circuit equipment M, conductor 389, working contact of armature 422 and the said armature, resting contact of armature 433 and the said armature, wiper 443, bank contact d 27, conductor 163, armature 521 and its working contact, and the low resistance secondary wlndlng of the induction coil of the busy signaling machine Q to battery. Bythe closure oi the above circuit the relay 109 is energized and performs the same functions as in the case where the called subscriber removes his receiver. Among other things, the left hand windings of the repeating coil are connected to enable the operator to hear the'busy signal, and also the high resistance relay 101 is substituted for the low resistance relay 100 in the circuit of the supervisory relay 9 at the cord circuit (it being assumed that the operator has restored her calling device key K Upon perceiving the busy signal the operator need not release the connection. but may restore her listening key K and then throw the key K thus leaving the connection to the but called line under the control of the supervisory lamp L. As soon as the line becomes idle the test relay 502 and the private magnet 509 deenergize, the side switch wipers are advanced to third position, and relay 505 is energized to transmit by cooperation with slow acting relay 504 the .necessary momentary impulse over conducline switch C of substation A to release (assuming that the line was busy as a calling line). When the busy signaling machine Q is disconnected by the deenergization of the test relay 502, the energizing circuit of relay 109 at the selector W is broken and the relay retracts its armatures. As a result the control circuit including the supervisory relay 9 is again completed by way of the line relay 100 and the relay 9 is accordingly operated to light the lamp L, a red lamp, preferably, whereby the operator is notified that the called line has become idle.

It has been stated before that certain second selectors of the main exchange local trunking system have access to the repeater F by way of the trunk conductors 165, 166, and 167, shown at the u per left hand cor ner of Fig. 3, whereby ocal subscribers in the main exchange are enabled to extend connections to subscribers in the branch exchange. I will now briefly describe one of these connections. For this purpose it will be assumed that a calling subscriber in the main exchange has established connection with the bank contacts, 180, 168, and 181, through the medium of automatic switching mechanisms which may consist of an individual line switch and a first and second selector switch. These switches may be similar in most respects to the line switch C and the selector switch E, Fig. '5.

Upon the completion of the connection to the bank contacts named above, the line relay 201 is energized over a circuit which may be traced as follows: ground at G, lower winding of line relay 201, lower springs of the reversing relay 200, and conductor, 165 to bank contact 181, thence by way of the lower selector wiper (not shown),

' the calling subscribers loop and the upper selector wiper (also not shown) to thebank contact 180, and thence by way of conductor 167 upper springs of the reversing relay 200, and the upper winding of the line relay 201 to battery. Upon attracting its arm ture, the line relay 201 completes the usual circuit for the slow acting release relay 202, which is then operated to complete a holding circuit as follows: ground at G working contact of armature 218 and the said armature, and conductor 166 to bank contacts 16S, whence the circuit extends back to relays in the selector switch and to the holding Winding of the individual line switch I which are maintained energized in the usual manner to prevent the release of the connection. The other circuits closed at the repeater F following its seizure by the selector and the energization of the line and re lease relays, including the operating or control circuit extending via conductor 23a to the incoming selector E at the branch exchange, have already been described, the operations being identical with those which take place whenthe repeater is seized from the toll selector 1V, with one exception, however, the relay 203, whose circuit can only be completed by way of conductor 161 and a toll second selector such as the selector W, obviously remains deenergized. Such being the case, immediately upon the energization of relay 208 of the repeater, the ringing generator Gen is bridged across the trunk conductors 233 and 235 as follows: conductor 235, armature 231 and its working contact, armature 228 and its resting contact, armature 217 and its resting contact, armature 221 and its resting contact, armature 219 and its resting contact, armature 22 1 and its resting contact, lamp L contact ,of. the ringin v interrupter. IR, generator Gen, ground the grounded exchange battery, the lower winding of the ring cutoff relay 207, resting contact of armature 218 and the said armature, the resting contact of armature 215 and the said armature, the resting contact of armature 226 and the said armature, and the working contact of armature 280 and the said armature to the conductor 283. Since the conductors 233 and 235 are open at the distant end of the trunk, however and remain open until the connection to the called line is established, no flow of ringing current will take place at present.

The calling subscriber may now proceed to dial the remaining digits in the number, the ones previously called having been effective to control the establishment of the connection as far as the repeater F, and the ones now to be called being those which control the operation of the selector E andthe connector H at the branch exchange. Under the control of the line relay 201 of the repeater F the connection is completed precisely as was described in the preceding pages where the toll operator called-the substation A. It is to be noted that during the transmission of each series of impulses to the branch exchange, the line relay 201 also sends impulses to the slow acting relay 205, relay 203 being deenergized. The circuit is as follows: ground atG armature 212 and its resting contact, armature 214 and its working contact, resting contact of arma- 

